Internal combustion engine provided with a supercharger

ABSTRACT

In a convention throttle-controlled internal combustion engine (1, 2) equipped with a supercharger which has the form of a compressor (10) provided with screw rotors (14, 15) arranged in a compression chamber, the supercharger is inactive at part engine loads. Since the engine normally operates at part loads for about 95% of its running time, efficiency is correspondingly poor. This drawback is overcome with the arrangement according to the invention in which the screw compressor (10) is provided on the inlet side (20) thereof with a capacity regulating device (22) which is operated by a gas pedal, or accelerator, and which when the engine is only partially loaded, is adjusted to a corresponding position in which the compressor (10) operates as an expander (3) of variable throttle effect on the engine inlet side (3) and transmits power to the engine, thereby replacing the conventional gas throttle.

BACKGROUND OF THE INVENTION

The present invention relates to an arrangement in a throttle-controlledinternal combustion engine equipped with a supercharger in the form ofan air compressor which comprises helical rotors (male and femalerotors) located in a compression chamber and which is connected via atransmission arrangement to the crankshaft of the vehicle engine.

Known arrangements of this kind suffer the drawback of poor efficiencywhen the compressor is working at partial load. Another drawbackencountered with such arrangements is that difficulties are encounteredwith regard to the mutual co-action between the supercharger and thefuel supply system. Furthermore, when passing from partial load to fullload, there is a delay before full charging pressure is reached.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a simplifiedarrangement of the aforesaid kind in which these drawbacks are avoided.

This object is achieved in accordance with the invention by means of anarrangement having the characteristic features set forth in the claims.

The invention is based on the concept that if a supercharger in the formof a screw compressor is provided on the compressor inlet side with acapacity regulating or control device, conventional with screwcompressors (c.f. for instance Swedish Patent Specification No. 198588), and the capacity is reduced the compressor will function as anexpander or expansion machine, in the same manner as a gas throttle willthrottle the engine suction inlet, and therewith transfer power to theengine. This can be achieved directly through the transmission, orindirectly by retarding the expansion machine, e.g. with the aid of acharging generator. The expansion effect can be increased by varying thetransmission between the engine and the screw rotor machine, such thatwhen the machine functions as an expander the transmission ratio ischanged so that the screw rotor machine has a lower transmission ratiothan when it functions as a compressor. This can readily be achieved byselectively effecting the drive through the male rotor when operated asan expander through the female rotor when operated as a compressor. Thisresults in a reduction in fuel consumption when running at partialengine loads and when idling. The requirement of a gas throttle iseliminated, and fuel can be supplied readily to the engine in a mannerwhich will also obviate the need for a conventional carburettor. Aparticularly important advantage is afforded when the arrangementincorporates a fuel supply device that has provided therein a pluralityof supply apertures which are arranged to be exposed in sequence by thecapacity regulating slide during its movement towards a fully open inletport. This results in a well balanced increase in the fuel supply inproportion to the increase in engine load. Another specific advantageafforded by the invention is that the air of combustion is often cooledduring its passage through the expansion machine, due to the expansionthat takes place at part engine loads. Consequently, if the load on theengine should suddenly be rapidly increased, subsequent to the machinehaving previously functioned as an expander machine at partial engineloads, the still cool combustion air (cooled by cold surfaces downstreamof the expander) is able to counteract knocking in the combustionchambers during this stepping-up period.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail with reference to twoexemplifying embodiments thereof illustrated in the accompanyingdrawings, in which

FIG. 1 is a sectional view of a first embodiment of the invention takenon the line I--I in FIG. 2;

FIG. 2 is a sectional view taken on the line II--II in FIG. 3;

FIG. 3 is a sectional view of a second embodiment taken on the lineIII--III in FIG. 4;

FIG. 4 is a sectional view taken on the line IV--IV in FIG. 3;

FIG. 5 is a sectional view taken on the line V--V in FIG. 3; and

FIG. 6 is the same sectional view showing the capacity regulator set atfull engine load.

DETAILED DESCRIPTION OF THE INVENTION

The embodiment illustrated in FIGS. 1 and 2 comprises a four-cylinderinternal combustion engine 1, incorporating a cylinder head 2, a suctioninlet manifold 3, suction inlet ducts 4, suction inlet valves 5, andexhaust valves 6.

The engine has no actual carburetor or gas throttle as such. Instead,the screw motor machine 10 is connected to the inlet manifold 3.Furthermore, the fuel jets 11 are located in the inlet ducts 4, whichare formed as venturi pipes, and the jets 11 are connected through apipe 12 to a fuel-containing float chamber 13.

The screw rotor machine incorporates two screw rotors, a male rotor 14and a female rotor 15, which are journalled for rotation in acompression chamber 16 and are connected to the engine crankshaft (notshown) via a belt pulley 18 mounted on the shaft 17 of one rotor, and adrive belt 19 which passes around the pulley.

The machine includes an inlet 20 which leads to an inlet port 21, theeffective area of which can be adjusted with the aid of a slide 22 whichis mounted in, and forms part of, the wall of the chamber 16 for slidingmovement parallel with the axes of the rotors 14, 15, said slide beingreferred to hereinafter as a capacity regulating slide and beingconnected to the gas pedal, or accelerator pedal 24 of the vehiclethrough a linkage system 23.

Screw rotor machines of this kind provided with capacity regulatingvalves adjacent the inlet port are well known to the art, and are founddescribed and illustrated in the patent literature. Reference can bemade in this latter regard to Swedish Patent Specification No. 219 243,which teaches alternative valve arrangements for the same purpose.

When the engine runs at partial engine loads, e.g. with the gas pedalreleased to an engine idling position, the screw rotor machine willfunction, in principle, as a gas throttle. Combustion air is drawn inthrough the inlet 20 and through the inlet port 21, which is adjusted toits smallest effective area by the slide 22, and enters the workingchamber of the machine 10 and into the rotor grooves formed in saidchamber, the air subsequently expanding in said grooves and departingthrough an outlet 25 to the suction inlet manifold 3 of the engine. Thecombustion air is drawn from the manifold 3 into the cylinder chambersof the engine, via the venturi inlet ducts 4, where fuel is entrained bysuction from the jets 11.

As opposed to the case when the throttle control is effected with theaid of a gas throttle, the energy in this case is obtained from themachine 10, which functions as an expanding machine and consequentlycontributes toward rotation of the crankshaft through the transmission18, 19.

The air is also cooled as it expands. Although only a very moderateeffect is achieved herewith, as also with the aforesaid contribution tothe crankshaft drive, the effect increases with increasing pressureconditions, such as when regarding engine speed at high enginerevolutions. When the load on the engine is rapidly increased (bydepressing the gas pedal) cold combustion air is momentarily deliveredto the engine, therewith counter-acting the knocking tendency of theengine during acceleration. In addition hereto there is obtained thefurther advantage that immediately the gas pedal is depressed and theeffective area of the port 21 subsequently widened, by movement of theslide 22 to the right in FIG. 1, a full charging pressure is applied tothe engine. Normally, when supercharging an engine in a conventionalmanner, the supercharger is engaged, or activated, when the gas pedal isdepressed and there is a delay of a second or two before the chargingpressure has built-up. In the embodiment illustrated in FIGS. 1 and 2fuel is supplied downstream of the screw rotor machine 10, which has theadvantage of enabling the fuel jets 11 to be located close to thesuction inlet valves 5. The embodiment illustrated in FIGS. 3-6 differsin this regard, since the fuel is supplied upstream of the screw rotormachine 10. This means that the screw rotor machine 10 operates withmoist air, which is particularly advantageous in those cases in whichthe machine is equipped with asynchronized rotors 14, 15, i.e. the onerotor is arranged to drive the other. A machine of this kind is muchsimpler and requires less space than a machine with synchronized rotors.The moist conditions also improves the cooling of the machine and, insome cases, the lubrication of the mutually contacting surfaces of therotor. The fuel is also mixed thoroughly with the air of combustionduring passage through the machine. As will be understood from thefollowing, the supply of fuel can be regulated readily and simply inresponse to the load on the engine, down to engine idling speeds, whichis an additional advantage.

In the embodiment illustrated in FIGS. 3 and 4, that part of the inlet20 in which the regulating slide 22 is located, including the endsurface of this slide, has the form of a venturi nozzle 30, seen in thedirection in which the air of combustion passes. Extending in thenarrowest part or throat of the nozzle 30, in the longitudinal directionof the slide, is a fuel delivery pipe 31, which passes from a fuel duct32 communicating with a float chamber 13. The pipe 31 extends into abore 33 with a certain amount of clearance in relation thereto, and isprovided with a series of fuel jets 34, 35, 36, or has fuel outletopenings distributed therealong. When the slide 22 occupies its engineidling position (FIG. 5), the nozzle 30 is adjusted to its smallesteffective area and the jets 35, 36 are covered by the wall of the bore33. Despite the amount of inflowing combustion air per unit of timebeing minimal, the rate of air flow in the nozzle 30 is sufficientlyhigh to entrain effectively by suction fuel from the jet 34, which islocated in the best position in the venturi nozzle arrangement. When theengine load is increased, the slide 22 is moved slightly to the right inFIG. 5, to a position in which the next jet 35 in line is also exposedand the port leading to the interior of the screw rotor is sufficientlylarge for the machine to begin to work as a compressor driven by thecrankshaft of the engine, via the belt 19 and the belt pulley 18, thislatter effect being more applicable at full engine load, which isreached when the slide 22 occupies a position in which the port isopened to a maximum and all three jets 34-36 are exposed.

The screw rotor machine operates with a built-in pressure ratio equal toone (1) which means that the machine will not operate optimally as acompressor. This is not of great importance, however, since a vehicleengine will not run at full power, e.g. with supercharging, more than atmost about 5% of the time. If the engine can be expected to run at fullload over a longer period of time, the machine may be advantageouslyprovided, in a known manner, with a control slide 40 for setting asuitable pressure ratio, as illustrated in FIGS. 3 and 4.

If additional fuel is required during acceleration, this can be achievedby supplying additional fuel to the screws with lower pressure in thecompressor mode of the machine, with a similar effect to that achievedwith an acceleration pump in a conventional carburetor system. Inaddition to the aforesaid advantages, the arrangement according to theinvention will also save fuel when driving a vehicle at part engineloads or when idling the engine, which is also beneficial from apollution aspect. The carburetor function is incorporated more or lessin the actual inventive arrangement, which results in considerablesavings, particularly since the embodiment according to FIGS. 1 and 2 iscomparable with the provision of an individual carburettor for eachcylinder.

The transmission means 18, 19 is arranged such that when the aircompressor operates in a compressor mode, the engine drives the aircompressor by the female rotor being coupled to the transmission drivemeans 18, 19, and when it is operated in an expander mode, it is drivingsaid engine by the male rotor being coupled to the transmission drivemeans 18, 19.

The invention can also be applied to fuel injection engines and dieselengines, both with two-stroke and four-stroke engine designs.

I claim:
 1. A throttle controlled internal combustion engine (1, 2)comprising:a supercharger in the form of an air compressor (10), saidair compressor comprising intermeshed helical screw rotors (14, 15)arranged in a compression chamber; said air compressor (10) having acapacity regulating means (22) on an air inlet side (20) thereof;control means coupled to said capacity regulating means (22) forregulating the power output of the engine, said control means includingmovable means for assuming positions corresponding to a partial engineload for adjusting said capacity regulating means (22) to correspondingpositions in which the function of said air compressor (10) is switchedto an expander mode with variable throttling effect on the sunctioninlet side (3) of the engine and substitutes for a gas throttle, saidair compressor (10) in said expander mode transferring power to theengine (1, 2); and said capacity regulating means including a valveslide means (22) arranged for axial movement in relation to said rotors(14, 15) and forming a movable wall part of said compression chamber ofsaid air compressor (10), and also forming a movable wall part of aradial inlet port means (21), said radial inlet port means including anozzle means (30) of variable area, said nozzle means (30) communicatingwith a fuel delivery means (31).
 2. The engine of claim 1, wherein saidfuel delivery means (31) comprises a plurality of fuel supply openings(34, 35, 36) arranged so as to be exposed sequentially by said valveslide means (23) of said capacity regulating means during movement ofsaid valve slide means (22) towards a position in which said inlet port(21) is fully open.
 3. The engine of claim 2, wherein said aircompressor (16) comprises a control slide means (40) on the outlet side(25) thereof for setting an internal pressure ratio of said aircompressor.
 4. The engine of claim 1, wherein said air compressor (16)comprises a control slide means (40) on the outlet side (25) thereof forsetting an internal pressure ratio of said air compressor.
 5. The engineof claim 4,wherein said helical rotors (14, 15) of said air compressor(10) comprise male and female rotors; and further comprising drive means(18, 19) selectively coupled to said rotors, said drive means includingmeans for driving said air compressor by said female rotor when said aircompressor operates in a compressor mode, and means for furnishing powerfrom said air compressor to said engine by said male rotor when said aircompressor operates in an expander mode.
 6. The engine of claim3,wherein said helical rotors (14, 15) of said air compressor (10)comprise male and female rotors; and further comprising drive means (18,19) selectively coupled to said rotors, said drive means including meansfor driving said air compressor by said female rotor when said aircompressor operates in a compressor mode, and means for furnishing powerfrom said air compressor to said engine by said male rotor when said aircompressor operates in an expander mode.
 7. The engine of claim2,wherein said helical rotors (14, 15) of said air compressor (10)comprise male and female rotors; and further comprising drive means (18,19) selectively coupled to said rotors, said drive means including meansfor driving said air compressor by said female rotor when said aircompressor operates in a compressor mode, and means for furnishing powerfrom said air compressor to said engine by said male rotor when said aircompressor operates in an expander mode.
 8. The engine of claim1,wherein said helical rotors (14, 15) of said air compressor (10)comprise male and female rotors; and further comprising drive means (18,19) selectively coupled to said rotors, said drive means including meansfor driving said air compressor by said female rotor when said aircompressor operates in a compressor mode, and means for furnishing powerfrom said air compressor to said engine by said male rotor when said aircompressor operates in an expander mode.